JP3544847B2 - Optical information reproducing method and apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical information reproducing method and apparatus in which a light spot traces an information track in which information is recorded as a pit row on an information carrier to read recorded information, and more particularly, to an optical information reproducing method and apparatus which are focused on a medium. Tracking control means for causing a light beam to travel along the center of the track.
[0002]
[Prior art]
In recent years, optical discs, such as DVDs, for optically recording and reproducing information have been receiving attention as information carriers for storing large volumes of video information and data information. Tracks are formed on this optical disc at a pitch of about 1 μm concentrically or spirally, and information is recorded on the tracks by utilizing local optical constants or changes in physical shape.
[0003]
In order to reproduce information from an optical disc in such a recording form with high quality, an optical information reproducing apparatus controls the focusing position of a light spot for reading information with high precision, and this light spot always traces on a track. I am trying to do it. The positioning control of the light spot is performed two-dimensionally, and the control in the optical axis direction is performed by the focus control means, and the control in the radial direction is performed by the tracking control means. For such control, feedback control for controlling the position of the light spot so as to cancel the difference between the target position of the light spot and the current position, that is, the amount of error, is used.
[0004]
Among them, various methods for detecting a tracking error signal required for tracking control using optical means have been devised, and among them, a method for obtaining information recorded on an information carrier from a main light spot for reproducing information has been devised. A phase difference method using a signal has already been put to practical use. The principle of this phase difference method is disclosed in Japanese Patent Application Laid-Open No. 52-93222.
[0005]
FIG. 5 is a diagram for explaining the principle of detecting tracking error information by the phase difference method. In the figure, (a) is a diagram showing the positional relationship between the information pits and the light spot, and shows how the light spot moves from t0 to t4. In the figure, the traveling position (a) of the light spot indicates the center of the reproduction target track. Point (A) indicates the left side of the center of the reproduction target track. Further, the point (c) indicates the right side of the reproduction target track.
[0006]
FIG. 5B shows photoelectric conversion means for detecting reflected light from the information carrier and converting it into an electric signal. This photoelectric conversion means is divided into the first to fourth photodetectors by a dividing line in a track tangential direction and a dividing line in a radial direction perpendicular to the track. Ideally, a far-field pattern of reflected light from a medium is obtained. The optical system is designed such that the center of the photodetector is formed at the center of the photodetector. The off-track amount is between two detection signals (A + C) and (B + D) obtained by adding diagonal components of the outputs (A, B, C, D) of the four divided photodetectors. A phase difference occurs in proportion. This is shown in FIGS. 5 (c), (d) and (e).
[0007]
FIG. 5C is a schematic diagram showing a state where the phase relationship between the two detection signals changes according to the scanning position of the light spot. The waveform on the left is a detection signal waveform when the light spot travels to the left of the pit center at the point (A) in FIG. 9A, and the phase of the detection signal (A + C) is higher than that of the detection signal (B + D). Shows how it is going. The middle waveform is a detection signal waveform when the light spot travels at the point (a), that is, the center of the track, and shows that the detection signal (A + C) and the detection signal (B + D) have the same phase. Further, the waveform on the right side is a detection signal waveform when the light spot travels on the right side of the pit center at point (c), that is, the detection signal (A + C) has a phase delayed from the detection signal (B + D). Is shown.
[0008]
FIG. 5D shows the phase difference between the detection signal (A + C) and the detection signal (B + D) according to the scanning position of the light spot. In the figure, the phase difference is indicated by the pulse width. A pulse on the + side indicates a case where the detection signal (A + C) is ahead of the detection signal (B + D), and a pulse on the − side is a case where the detection signal (A + C) is behind the detection signal (B + D). Show. When the detection signal (A + C) and the detection signal (B + D) have the same phase, no pulse is output on both the + and-sides.
[0009]
FIG. 5 (e) illustrates the width of the pulse with respect to the traveling position of the light spot, that is, the amount of phase difference, and shows how the amount changes in proportion to the off-track amount from the track center. This phase difference is converted into an electric signal to obtain a tracking error signal required for tracking control.
[0010]
Here, it is known that an offset (hereinafter, referred to as a first offset) occurs in the tracking error signal depending on the pit depth. For details, see “Development of Learning Control Method for High Accuracy in DVD-ROM Drive”, IEICE Technical Report OPE96-150, p. P. 33-38.
[0011]
FIG. 6 shows the principle of generation of this offset. The figure shows the output waveforms (A to D) of the quadrant detector when the light beam is located at the pit end on the track center, and the pit depth and the presence or absence of a lens shift are used as parameters. .
[0012]
When the pit depth is λ / 4 (where λ indicates the wavelength of the LD), waveform patterns appearing in the (A + C) signal and the (B + D) signal obtained from the photodetector divided in the semi-meridian direction of the disk Is the same, even if the lens moves and the light spot on each photodetector moves, the position generated between the (A + C) signal and the (B + D) signal when the light spot is on the track center. The phase difference becomes zero.
[0013]
On the other hand, when the pit depth is different from λ / 4, a level difference occurs between the (A + C) signal and the (B + D) signal. When the reflected light on the photodetector does not move, there is no level difference between the (A + C) signal and the (B + D) signal, and the tracking error signal becomes zero. However, when the lens moves, an imbalance occurs between the (A + C) signal and the (B + D) signal. As a result, a phase difference occurs and a first offset occurs in the tracking error signal.
[0014]
Next, a conventional optical information reproducing apparatus for obtaining a tracking error signal using the phase difference method having such characteristics will be described with reference to FIG. In the figure, 1 is an information carrier, 2 is an optical head, 3 is a first phase adjusting means, 4 is a second phase adjusting means, 5 is a phase adjusting amount setting means, 6 is a phase difference detecting means, and 7 is an offset. Correction learning means, 8 is tracking control means, 9 is first switch means, and 10 is a driver. Further, the optical head 2 includes a laser diode (hereinafter abbreviated as LD) 21, a beam splitter (hereinafter abbreviated as BS) 22, an actuator 23, a lens 24, and a photoelectric conversion unit 25. The phase difference detecting means 6 includes a first adding means 61, a second adding means 62, a first comparator 63, a second comparator 64, a phase comparing means 65, and a phase difference-voltage converting means 66. You. Further, the offset correction learning means 7 includes a waveform symmetry measuring means 71 and a controller 72.
[0015]
The operation of the conventional optical information reproducing apparatus configured as described above will be described with reference to FIG. The light output from the LD 21 constituting the optical head 2 is controlled by a laser power control means (not shown) so that the power on the information carrier 1 becomes a predetermined power. The light beam emitted from the LD 21 is shaped into parallel light by a collimator (not shown) constituting the optical head 2 and then enters the BS 22. The BS 22 has a property of transmitting light incident from the LD 21 side and reflecting light from the information carrier 1 side. The light beam transmitted through the BS 22 is focused on the center of the information track on the information carrier 1 by the lens 24 controlled by the actuator 23.
[0016]
The light reflected by the information carrier 1 passes through the lens 24 again, is reflected by the BS 22, and enters the photoelectric conversion unit 25. The photoelectric conversion means 25 is divided into four parts by a division line in the track tangential direction and a division line in the radial direction perpendicular to the track, and is divided into four pits formed on the information carrier 1. The reflected light from the information carrier containing information is detected and converted into an electric signal.
[0017]
In this division, in the ideal state where the light spot traces the center of the track formed with the pit depth of λ / 4, the center of the far field pattern of the light reflected from the information carrier 1 is the photoelectric conversion means 25. Designed to be formed in the center of The positional relationship between the first to fourth photodetectors is such that the first and second photodetectors are arranged on one side and the third and fourth photodetectors are arranged on the other side in the vertical direction. . Further, the first and third light detectors are arranged at diagonal positions, and the second and fourth light detectors are arranged at the other diagonal position.
[0018]
Between two detection signals (A + C) and (B + D) obtained by adding the diagonal components of the outputs A, B, C, and D of the first to fourth photodetectors thus divided into four. The optical system is designed so that a phase difference proportional to the off-track amount occurs.
[0019]
However, as described above, when the pit depth is different from λ / 4, a phase difference occurs due to imbalance between the (A + C) signal and the (B + D) signal, and this becomes the first offset of the tracking error signal. In order to cancel the first offset, the conventional optical information reproducing apparatus uses the first phase adjusting unit 3 and the second phase adjusting unit 4 to output the output A of the first photodetector and the second photodetector. The output B of the detector is adjusted in phase, and the phase relationship between the output C of the third photodetector and the output D of the fourth photodetector is adjusted.
[0020]
The optimum value of the phase adjustment amount changes depending on the pit depth. Therefore, the phase adjustment amount set by the first phase adjustment unit 3 and the second phase adjustment unit 4 is adjusted by the offset correction learning unit 7 and the phase adjustment amount setting unit 5 described below to obtain the best tracking error signal. Is controlled to a value that can be obtained.
[0021]
The phase difference detecting means 6 includes an output A ′ of the first phase adjusting means 3, an output B ′ of the second phase adjusting means 4, an output C of the third photodetector, and an output C of the fourth photodetector. A tracking error signal is detected from each signal of the output D by performing the following processing.
[0022]
The first adder 61, which is a component of the phase difference detector 6, detects the output A 'of the first phase adjuster 3 and the third photodetector arranged diagonally to the first photodetector. After adding the output C, the first comparator 63 binarizes the output. After the output B 'of the second phase adjusting means 4 and the output D of the fourth photodetector arranged diagonally to the second photodetector are added by the second adding means 62, Binarization is performed by a second comparator 64.
[0023]
Then, the phase difference between the two binarized signals of the first comparator 63 and the second comparator 64 is detected by the phase comparing means 65, and is converted into an electric signal through the phase difference-voltage converting means 66, whereby the phase difference tracking is performed. Detect an error signal. In the conventional example, a low-pass filter (hereinafter abbreviated as LPF) is used as the phase difference-voltage conversion means 66.
[0024]
The tracking error signal detected as described above is input to the offset correction learning means 7 and the tracking control means 8. The offset correction learning means 7 first measures the symmetry of the tracking error signal by the waveform symmetry measuring means 71. Then, the controller 72 sets the phase adjustment amounts of the first phase adjustment unit 3 and the second phase adjustment unit 4 via the above-described phase adjustment amount setting unit 5 so that the symmetry becomes the best. At this time, the offset correction learning algorithm follows the procedure shown in FIG.
[0025]
When the offset correction learning mode is activated (S1), the controller 72 controls the first switch means 9 and inputs the output of the controller 72 to the driver 10. As a result, the tracking control becomes inoperative, and the lens 24 is driven inward by the control of the controller 72 (S2). In this state, the controller 72 controls the first phase adjusting unit 3 and the second phase adjusting unit 4 via the phase adjusting amount setting unit 5 to determine the phase adjusting amount at which the tracking error signal has the best symmetry. It is determined (S3).
[0026]
Next, the controller 72 drives the lens 24 to the outer peripheral side (S4). In this state, the controller 72 controls the first phase adjusting unit 3 and the second phase adjusting unit 4 via the phase adjusting amount setting unit 5 to determine the phase adjusting amount at which the tracking error signal has the best symmetry. It is determined (S5).
[0027]
Finally, the controller 72 determines a phase adjustment amount that minimizes the difference in symmetry of the tracking error signal from the inner and outer best phase adjustment amounts determined in S3 and S5, and a first phase adjustment unit. The values are set in the third and second phase adjusting means 4 (S6), and the offset correction learning mode is ended (S7).
[0028]
When the offset correction learning mode ends, the controller 72 switches the first switch 9 and inputs the output of the tracking control means 8 to the driver 10. The tracking control means 8 controls the lens 24 in the radial direction via the driver 10 and the actuator 23 so as to cancel the tracking error detected by the phase difference detection means 6, and the light beam emitted from the optical head to the information carrier. Is controlled to trace on the center of the track.
[0029]
[Problems to be solved by the invention]
As described above, the conventional optical information reproducing apparatus uses the waveform symmetry of the tracking error signal as information for judging the best value of the phase adjustment amount by the phase adjusting means, that is, the amount of deviation between the center level of the reproduced waveform and the reference level. Is used. In order to measure the center level of the reproduced waveform, it is necessary to find the maximum point and the minimum point of the tracking error signal. As means for obtaining the maximum point and the minimum point, for example, an analog-to-digital conversion circuit (hereinafter abbreviated as ADC) discretely samples a signal level and then digitally processes the signal level. Measuring means for detecting the peak and bottom envelopes and obtaining the midpoint is used. First, in the measuring means using the ADC, a case is supposed in which the local maximum point and the local minimum point, which are instantaneous values, are measured based on the sampling rate, instead of the local points. In this case, the measured midpoint between the maximum point and the minimum point includes a measurement error, and the quality of the tracking error signal is degraded. Attempting to suppress this measurement error by using a high-speed ADC may lead to an increase in device cost. Further, if it is attempted to suppress the above measurement error by analog means, two systems of envelope measurement circuits are required, which may lead to an increase in circuit scale.
[0030]
Next, the conventional optical information reproducing apparatus also has a problem that an electric offset generated in a circuit after the phase comparator cannot be canceled. This problem means that it is not possible to clarify whether the offset error of the tracking error signal is caused by the electrical offset or the first offset caused by the improper setting of the phase adjustment means. There is also a possibility that the quality of the tracking error signal is reduced by the correction learning.
[0031]
Further, since the conventional optical information reproducing apparatus cannot adjust the signal amplitude of the tracking error signal to a predetermined value, it cannot correct the gain fluctuation of the entire tracking control system due to the characteristic variation of the optical head, the information carrier, and the circuit. There is also a concern that the performance may be degraded.
[0032]
The present invention has been made to solve the above problems, and a first object is to change only a combination of input signals to a phase comparison means of a tracking error signal detection circuit by a phase difference method. An optical system that can set the phase adjustment amount adjusted by the phase adjustment unit to each output signal of the photoelectric detector to the best value without substantially affecting the device cost and without deteriorating the quality of the tracking error signal. The object is to obtain an information reproducing method and apparatus.
[0033]
A second object is to provide an optical information reproducing method and apparatus capable of canceling an electric offset in addition to the first object.
A third object is to provide a means for setting the reproduction amplitude of the tracking error signal to a predetermined level.
[0034]
[Means for Solving the Problems]
An optical information reproducing apparatus according to the present invention comprises:
An optical information reproducing apparatus in which a light spot traces an information track recorded as an information pit string on an information carrier and reads recorded information,
Dividing a far field pattern of light reflected by the information carrier in a direction perpendicular to a tangential direction of the information track, and disposing a first photodetector and a second photodetector in one of the vertically divided ones; A third photodetector is arranged on the other vertically divided side so as to be diagonal to the first photodetector, and a fourth photodetector is arranged diagonally to the second photodetector. Photoelectric conversion means in which a photodetector is arranged;
First to fourth phase adjusting means for individually adjusting the phase of each of the outputs from the first to fourth photodetectors;
Offset correction learning means for adjusting the first to fourth phase difference adjustment means,
A first sum signal obtained by adding an output from the first phase adjusting unit and an output from the second phase adjusting unit; an output from the third phase adjusting unit and a signal from the fourth phase adjusting unit. Or the third sum signal obtained by adding the output from the first phase adjusting means and the output from the third phase adjusting means to the second sum signal obtained by adding the outputs of the second sum signal and the second sum signal. Phase difference detection means for detecting a phase difference between an output from the phase adjustment means and a fourth sum signal obtained by adding the outputs from the fourth phase adjustment means;
Switching means for switching whether the phase difference detection means detects the phase difference between the first sum signal and the second sum signal or the third sum signal and the fourth sum signal; Prepare,
When adjusting the first to fourth phase difference adjusting means, the switching means selects the first sum signal and the second sum signal as targets for detecting the phase difference by the phase difference detecting means. Then, the first to fourth phase difference adjusting means are adjusted by the offset correction learning means so as to cancel the phase difference output from the phase difference detecting means,
When the tracking error information is obtained, the switching means selects the third sum signal and the fourth sum signal as targets for detecting the phase difference by the phase difference detecting means.And
The offset correction learning means,
Offset adjustment means for adjusting the electrical offset superimposed on the output from the phase difference detection means,
Offset measuring means for measuring an output from the offset adjusting means and obtaining an electrical offset,
Reproduction level measuring means for measuring the output amplitude from the offset adjusting means,
A control unit for controlling the phase difference detection unit, the offset adjustment unit, and the phase adjustment unit based on an output from the offset measurement unit and an output from the reproduction level measurement unit.
It is characterized by the following.
[0036]
Further, the offset correction learning means,
Offset adjustment means for adjusting the electrical offset superimposed on the output from the phase difference detection means,
Offset measuring means for measuring an output from the offset adjusting means and obtaining an electrical offset,
Reproduction level measuring means for measuring the output amplitude from the offset adjusting means,
The apparatus further comprises control means for controlling the phase difference detecting means, the offset adjusting means, and the phase adjusting means based on an output from the offset measuring means and an output from the reproduction level measuring means.
[0037]
Further, the phase difference detecting means detects the phase difference between the signals by the phase comparing means, converts the phase difference into a voltage by the LPF, and varies the gain of the LPF to change the conversion gain of the phase difference into a voltage. It is configured to change.
[0038]
Further, the phase difference detecting means detects the phase difference between the two signals by the phase comparing means, converts the phase difference into a voltage by the charge pump and the LPF, and varies the drive current of the charge pump or the gain of the LPF. Thus, a configuration is provided in which the conversion gain for converting the phase difference into a voltage is changed.
[0039]
Initializing when the offset correction learning mode is started; and dividing the far field pattern of the light reflected by the information carrier in the tangential direction and the vertical direction of the information track, and dividing the far field pattern in the vertical direction. A first photodetector and a second photodetector, and a third photodetector disposed on the other of the vertically divided sides so as to be diagonally positioned with respect to the first photodetector. , A fourth photodetector arranged so as to be diagonally positioned with respect to the second photodetector, and first to first individually adjusting the phases of the respective outputs from the first to fourth photodetectors. In the fourth phase adjustment output, a first sum signal obtained by adding the first phase adjustment output and the second phase adjustment output, the third phase adjustment output, and the fourth phase adjustment output are added. Selecting a first phase comparison mode for detecting a phase difference with the second sum signal;
Driving the lens in one direction of the inner and outer peripheries of the information carrier;
Detecting a phase difference in the first phase comparison mode;
The phase of the output from the first to fourth photodetectors so that the output from the step of detecting the phase difference in the first phase comparison mode cancels the phase difference detected in the first phase comparison mode. A one-way adjustment step of adjusting each of
Driving the lens in the other direction on the inner and outer circumferences of the information carrier;
Driving in the other direction to cancel the phase difference detected in the first phase comparison mode by the output from the step of detecting the phase difference in the first phase comparison mode. A different direction adjustment step of adjusting each of the phases of the output from the photodetector,
A step of adjusting an adjustment amount in the one-direction adjustment step and the other-direction adjustment step.
After the step of adjusting the adjustment amount in the one-direction adjustment step and the other-direction adjustment step,
Phase difference between a third sum signal obtained by adding the first phase adjustment output and the third phase adjustment output, and a fourth sum signal obtained by adding the second phase adjustment output and the fourth phase adjustment output Selecting a second phase comparison mode for detecting
Adjusting the amplitude of the tracking error signal,
The step of performing the initial setting,
Detecting a phase difference between a third sum signal obtained by adding the first phase adjustment output and the third phase adjustment output, and a fourth sum signal obtained by adding the second phase adjustment output and the fourth phase adjustment output; Selecting a second phase comparison mode to perform;
Adjusting the reproduction level of the phase difference output detected in the second phase comparison mode to be within an allowable value;
Adjusting the electrical offset superimposed on the phase difference output to be within an allowable value.Things.

[0040]
Furthermore, the step of performing the initial setting includes:
Detecting a phase difference between a third sum signal obtained by adding the first phase adjustment output and the third phase adjustment output, and a fourth sum signal obtained by adding the second phase adjustment output and the fourth phase adjustment output; Selecting a second phase comparison mode to perform;
Adjusting the reproduction level of the phase difference output detected in the second phase comparison mode to be within an allowable value;
Adjusting the electrical offset superimposed on the phase difference output so as to be within an allowable value.
[0042]
The present invention uses the above means and has the following effects.
By setting the phase adjustment amount of the first to fourth phase adjustment means to a value at which the phase difference generated between the first sum signal and the second sum signal is canceled, the pit depth and the lens position can be adjusted. Deterioration in quality of the track error signal caused by the dependence is suppressed, and tracking error information is obtained from a phase difference generated between the third sum signal and the fourth sum signal.
[0043]
Further, by switching the object to be compared by the phase comparing means, a first offset or tracking error signal which varies depending on the pit depth and the lens position, which is a problem in obtaining a tracking error signal by the phase difference method. Can be directly detected.
[0044]
Furthermore, by adding a function to correct the gain offset of the tracking control system caused by the electrical offset caused by the circuit and the variation in the characteristics of the optical head and the circuit, which cause the quality of the tracking error information to be reduced, a high quality tracking error signal can be obtained. Get.
[0045]
Further, the phase difference-voltage means is constituted by an LPF, and the gain of the tracking control system can be adjusted by changing the LPF gain.
[0046]
Further, the phase difference-voltage means is constituted by a charge pump and an LPF, and the conversion gain setting means is constituted by varying the drive current of the charge pump and the gain of the LPF, so that the entire gain of the tracking control system can be adjusted. And
[0047]
Further, in order to suppress the influence of the lens position and uniquely determine the phase adjustment of the first to fourth phase adjusting means, the lens is forcibly driven to the inner side and the outer side in the radial direction, and the first and second phases are adjusted. And a method for obtaining the phase difference adjustment amount that can minimize the phase difference between the sum signals of the above.
[0048]
Further, a method is provided for canceling an electrical offset superimposed on the tracking error signal, suppressing a fluctuation in the amplitude of the tracking error signal due to a variation in the characteristics of each block constituting the method, and improving the reliability of the tracking control system. I do.
[0049]
Further, after canceling the first offset superimposed on the tracking error signal due to the pit depth or the lens position, the phase difference between the third and fourth sum signals is detected, and the electric signal is output at an arbitrary gain. To obtain a tracking error signal.
[0050]
BEST MODE FOR CARRYING OUT THE INVENTION
In an optical information reproducing method and apparatus according to an embodiment of the present invention, a tracking control system that controls a light spot to trace the center of a track by using a tracking error signal based on a phase difference method includes: Photoelectric conversion means comprising a four-division detector for converting light into an electric signal; four phase adjustment means for individually adjusting the phase of the output signal of the photoelectric conversion means; and a phase adjustment amount of the four phase adjustment means are set. Between two phase-divisional or radial signals of a four-division detector from the output of each phase adjustment means. A first offset of a tracking error signal or a first offset of the tracking error signal caused by reproducing an information carrier having a pit depth different from λ / 4 is directly detected from the phase difference. A phase difference detection unit, an offset correction learning unit that sets an adjustment amount of the phase adjustment unit via a phase adjustment amount setting unit, and a light spot centered on the information track using the tracking error signal detected by the phase difference detection unit. Tracking control means for controlling the tracing of the phase adjustment means, the offset correction learning means sets the phase adjustment amount of the phase adjustment means to the best value in a learning manner, thereby changing the phase adjustment amount depending on the pit depth. The first offset can be canceled, and an offset-free and highly reliable tracking control system can be constructed.
[0051]
Further, in an optical information reproducing method and apparatus according to another embodiment of the present invention, a tracking control system that controls a light spot to trace the center of a track by using a tracking error signal by a phase difference method includes: Photoelectric conversion means comprising a four-division detector for converting the reflected light from the carrier into an electric signal; four phase adjustment means for individually adjusting the phase of the output signal of the photoelectric conversion means; and the phases of the four phase adjustment means Phase adjustment amount setting means for setting an adjustment amount, and two pairs of two signals corresponding to diagonal components of a four-division detector or two pairs corresponding to detectors divided in a radial direction from outputs of the respective phase adjustment means. A phase comparing means for detecting a phase difference between two added signals obtained by selecting and adding one of the two signals, and an output of the phase comparing means to a conversion gain setting means Phase difference-voltage conversion means for converting the output signal of the phase difference-voltage conversion means into a voltage signal with the set gain, and offset correction learning means for measuring the amplitude of the output signal of the phase difference-voltage conversion means and canceling the offset in a learning manner. With this arrangement, it is possible to remove the electrical offset generated in the output of the phase difference-voltage conversion means by the offset correction learning means in a state where the operation of the phase comparison means is stopped. By setting the amount of phase adjustment of the phase adjusting means to the best value, two pairs of two signals corresponding to the detector divided in the radial direction of the four-split detector are selected from the output of each phase adjusting means and added. A conversion gain setting step can be performed so that the phase difference between the two added signals obtained can be canceled and the reproduction level of the tracking error signal becomes a predetermined level. , The conversion gain of the phase difference-voltage conversion means can be adjusted, so that there is no first offset depending on the pit depth or electrical offset generated in the circuit, and a tracking error signal having a predetermined amplitude level can be obtained. Thus, the reliability of the tracking control system can be improved.
[0052]
Furthermore, a desired conversion gain can be obtained by configuring the phase difference-voltage conversion means with a charge pump and an LPF and configuring the conversion gain setting means with a variable drive current for the charge pump.
[0053]
In addition, a desired conversion gain can be obtained by configuring the phase difference-voltage conversion means with a charge pump and an LPF, and configuring the conversion gain setting means with a variable gain of the LPF.
[0054]
Hereinafter, the present invention will be specifically described with reference to the drawings showing the embodiments.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an optical information reproducing apparatus according to Embodiment 1 of the present invention. In FIG. 1, 1 is an information carrier, 2 is an optical head, 3 is a first phase adjusting means, 4 is a second phase adjusting means, 5 is a phase adjusting amount setting means, 6 is a phase difference detecting means, and 7 is an offset. Correction learning means, 8 is tracking control means, 9 is first switch means, 10 is a driver, 11 is third phase adjustment means, and 12 is fourth phase adjustment means. Further, the optical head 2 includes an LD 21, a BS 22, an actuator 23, a lens 24, and a photoelectric conversion unit 25. The phase difference detecting means 6 includes a first adding means 61, a second adding means 62, a first comparator 63, a second comparator 64, a phase comparing means 65, a phase difference-voltage converting means 66, a second Of the switch means 67. Furthermore, the offset correction learning means 7 includes a controller 72 and an offset measuring means 73.
[0055]
Next, the operation of the optical information reproducing apparatus according to the first embodiment will be described with reference to FIG. The optical output from the LD 21 constituting the optical head 2 is controlled by a laser power control means (not shown) so as to have a predetermined power on the information carrier 1. The light beam emitted from the LD 21 is shaped into parallel light by a collimator (not shown) constituting the optical head 2 and then enters the BS 22. The BS 22 has a characteristic of transmitting light incident from the LD 21 side and reflecting light from the information carrier 1 side. The light beam transmitted through the BS 22 is focused on the center of the information track on the information carrier 1 by the lens 24 controlled by the actuator 23.
[0056]
The light reflected by the information carrier 1 passes through the lens 24 again, is reflected by the BS 22, and enters the photoelectric conversion unit 25. The photoelectric conversion means 25 is divided into four parts by first to fourth photodetectors, and is tangential to a track by a far field pattern of light reflected from the information carrier including pit information formed on the information carrier 1. The optical signal in each area divided into four in the direction and the radial direction perpendicular to the direction is detected and converted into an electric signal.
[0057]
In this division, in the ideal state where the light spot traces the center of the track formed with the pit depth of λ / 4, the center of the far field pattern of the light reflected from the information carrier 1 is the photoelectric conversion means 25. Designed to be formed in the center of The positional relationship between the first to fourth photodetectors is such that the first and second photodetectors are arranged on one side and the third and fourth photodetectors are arranged on the other side in the vertical direction. . Further, the first and third light detectors are arranged at diagonal positions, and the second and fourth light detectors are arranged at the other diagonal position.
[0058]
Between two detection signals (A + C) and (B + D) obtained by adding the diagonal components of the outputs A, B, C, and D of the first to fourth photodetectors thus divided into four. The optical system is designed so that a phase difference proportional to the off-track amount occurs.
[0059]
However, as described above, when the pit depth is different from λ / 4, a level difference occurs between the (A + B) signal and the (C + D) signal, and the movement of the lens 24 causes the (A + C) signal and the (B + D) signal to move. 2.) An imbalance occurs between the signals, which causes a first offset in the tracking error signal, and consequently deteriorates the tracking control performance. In order to eliminate the imbalance generated between the (A + C) signal and the (B + D) signal, the first phase adjusting means 3, the second phase adjusting means 4, the third phase adjusting means 11, and the fourth phase The adjustment unit 12 determines the phase relationship between the output A of the first photodetector, the output B of the second photodetector, the output C of the third photodetector, and the output D of the fourth photodetector. adjust.
[0060]
The optimum value of the phase adjustment amount changes depending on the pit depth, and also changes depending on the reproduction speed. Therefore, the phase adjustment amount of each phase adjustment unit needs to be set to a value at which the best tracking error signal can be obtained by the offset correction learning unit 7 and the phase adjustment amount setting unit 5 described later. In the present embodiment, this is realized by obtaining a phase adjustment amount at which the phase difference between the (A + B) signal and the (C + D) signal becomes zero. The operation for optimizing the amount of phase adjustment of each phase adjusting unit will be described below.
[0061]
The controller 72 controls the second switch means 67 to select an input signal to the first addition means 61 and the second addition means 62. By this selection, the output B 'of the second phase adjusting means 4 is applied to one input of the first adding means 61, and the output B of the third phase adjusting means 11 is applied to one input of the second adding means 62. C 'is input. The first adder 61 has the other input connected to the output A 'of the first phase adjuster 3, and outputs (A' + B ') as a result. The second addition means 62 has the other input connected to the output D 'of the fourth phase adjustment means 12, and outputs (C' + D ') as a result.
[0062]
The first comparator 63 binarizes the output (A '+ B') of the first adding means 61, and the second comparator 64 converts the output (C '+ D') of the second adding means 62 to binary. Become The phase comparison means 65 detects a phase difference between the output of the first comparator 63 and the output of the second comparator 64. The output of the phase comparison means 65 is time information, which is converted into an electric signal by the phase difference-voltage conversion means 66. (The above operation is abbreviated as mode 1.)
[0063]
The output of the phase difference-voltage converter 66 provides information for optimizing the amount of phase adjustment of each phase adjuster. That is, when the phase adjustment amount is set to the optimum value, the output of the phase difference-voltage conversion unit 66 becomes zero regardless of the lens position. On the other hand, if the phase adjustment amount is not the optimum value, a first offset occurs in the output of the phase difference / voltage conversion unit 66 depending on the lens position.
[0064]
Therefore, the optimum phase adjustment amount of each phase adjusting means is monitored by the offset measuring means 73 constituting the offset correction learning means 7 by monitoring the output of the phase difference-voltage converting means 66, and the output value is zero regardless of the lens position. This can be derived by the controller 72 learningly controlling the phase adjustment amount of each phase adjustment unit via the phase adjustment amount setting unit 5.
[0065]
The control of the lens position at this time is realized by the controller 72 controlling the first switch means 9 and driving the driver 10 of the actuator 23 for controlling the radial position of the lens 24 by the output of the controller 72. . The offset correction learning algorithm at this time takes the procedure shown in FIG.
[0066]
When the offset correction learning mode is activated (S10), the drive controller that controls the entire apparatus (not shown) sets an initial value parameter in the drive (S11), turns on the LD, and then focuses the light spot on the information carrier. The operation is performed up to the control (S12). Then, the controller 72 selects the mode 1, controls the first switch means 9 to use the output of the controller 72 as an input signal to the driver 10, and controls the second switch means 67 to set the first The output B 'of the second phase adjusting means 4 and the output C' of the third phase adjusting means 5 are set to be input to the adding means 67 and the second adding means 68, respectively (S13).
[0067]
Thereafter, the lens 24 is driven inward by the control of the controller 72 (S14). In this state, the output level of the phase difference / voltage conversion unit 66 is detected by the offset measurement unit 73 (S15), and the controller 72 determines whether or not the result satisfies the allowable value (S16).
[0068]
If the determination result does not satisfy the allowable value, the controller 72 individually changes the phase adjustment amount of each phase adjustment unit via the phase adjustment amount setting unit 5 (S17), and again outputs the output level of the phase difference-voltage conversion unit 66. Returns to the step of detecting (S15). In this way, by repeating the loop of S15 → S16 → S17 → S15 until the determination result satisfies the allowable value, the optimum amount of phase adjustment for each phase adjusting means when the lens is displaced inward is obtained. Then, the value is stored (S18).
[0069]
Next, the controller 72 drives the lens 24 to the outer peripheral side (S19). In this state, the output level of the phase difference-voltage conversion means 66 is detected by the offset measuring means 73 (S20), and the controller 72 determines whether or not the result satisfies an allowable value (S21).
[0070]
If the determination result does not satisfy the allowable value, the controller 72 individually changes the phase adjustment amount of each phase adjustment unit via the phase adjustment amount setting unit 5 (S22), and again outputs the output level of the phase difference-voltage conversion unit 66. Returns to the step of detecting (S20). In this way, by repeating the loop of S20 → S21 → S22 → S20 until the determination result satisfies the allowable value, the optimum amount of phase adjustment for each phase adjusting means when the lens is displaced to the outer peripheral side is obtained. Then, the value is stored (S23).
[0071]
The difference between the inner-side optimum phase adjustment amount and the outer-side optimum phase adjustment amount stored for each phase adjusting means is determined, and it is determined whether or not the difference satisfies an allowable value (S24). If the determination result does not satisfy the allowable value, the controller 72 obtains an average value of the inner peripheral side optimal phase adjustment amount and the outer peripheral side optimal phase adjustment amount stored for each phase adjusting unit, and the like. This value is set to each phase adjusting means via (S25). After the setting, the process returns to S14, and the operations of S14 to S25 are repeated until the difference between the inner peripheral side optimal phase adjustment amount and the outer peripheral side optimal phase adjustment amount satisfies an allowable value. When the allowable value is satisfied, the offset correction learning mode is started. The process ends (S26).
[0072]
After optimizing the amount of phase adjustment of each phase adjusting means as described above, the operation shifts to an operation of detecting a tracking error signal. The controller 72 controls the second switch means 67 to exchange the input signals to the first addition means 61 and the second addition means 62, and one input of the first addition means 61 has a third phase adjustment. The output C ′ of the means 11 and the output B ′ of the second phase adjusting means 4 are input to one input of the second adding means 62. As a result, the first adding means 61 outputs (A '+ C'). Further, the second adding means 62 outputs (B '+ D').
[0073]
The first comparator 63 binarizes the output (A '+ C') of the first adding means 61, and the second comparator 64 converts the output (B '+ D') of the second adding means 62 to binary. Become The phase comparison means 65 detects a phase difference between the output of the first comparator 63 and the output of the second comparator 64. The output of the phase comparison means 65 is time information, which is converted into an electric signal by the phase difference / voltage conversion means 66 to obtain a tracking error signal by a phase difference method.
[0074]
The tracking error signal indicates the difference between the target position and the current position of the light spot, that is, the error amount (off-track amount), and the tracking control means 8 controls the light spot position so as to cancel the error amount. The control of the light spot position is realized by the driver 10 driving the actuator 23 based on the output of the tracking control means 8 to control the position of the lens 24 in the radial direction. Therefore, the controller 72 sets the output of the tracking control unit 8 via the first switch unit 9 so as to be input to the driver 10.
[0075]
In FIG. 1, the second switch means 67 is arranged between the second and third phase adjusting means and the first and second adding means. However, the present invention is not limited to this. It suffices if a phase difference between ') and (C' + D ') or a phase difference between (A' + C ') and (B' + D ') can be detected. In this sense, the same effect can be obtained even if the configuration from the output of the phase adjustment unit to the phase comparison unit 65 is changed as follows. The first point is that the required two signals are selected after the addition signal is obtained by the four adding means and input to the first and second comparators. The second point is that the four adding means and the four After a binary signal corresponding to the addition signal is obtained by a comparator, two necessary signals are selected and input to the phase comparison means 65.
[0076]
The phase difference-voltage conversion means 66 may have any configuration as long as it converts time information, which is a phase difference, into an electric signal, and is generally a low-pass filter (hereinafter abbreviated as LPF). It can also be realized simply by smoothing. As another configuration, a method including a charge pump and an LPF has been put to practical use.
[0077]
Further, the offset correction learning means 7, the tracking control means 8 and the first switch 9 are a digital signal processor (hereinafter abbreviated as DSP) with a built-in ADC and digital-analog conversion circuit (hereinafter abbreviated as DAC). It is also possible to realize.
[0078]
In the optical information reproducing method and apparatus configured as described above, by switching the object to be compared by the phase comparing means 65, the pit depth and the lens position, which are problems in obtaining the tracking error signal by the phase difference method, are obtained. The first offset or the tracking error signal that changes depending on the information can be directly detected, and the amount of phase adjustment of each phase comparison means can be optimized by learning repetitive control based on this information, so that offset-free tracking can be performed. An error signal detection system can be realized, and the reliability of the device is improved. In addition, since the first offset itself can be measured as a voltage value instead of obtaining the first offset from the waveform symmetry of the tracking error signal as in the related art, the ADC for measurement is not an expensive high-speed type. Does not impair the detection accuracy. In addition to this, an increase in hardware is small, so that an increase in device cost can be suppressed.
[0079]
Further, the setting of the optimum phase adjustment amount of each phase adjusting unit that changes according to the reproduction speed can be dealt with by the above-described offset correction learning algorithm without changing hardware.
[0080]
Embodiment 2 FIG.
FIG. 3 is a block diagram showing an optical information reproducing apparatus according to Embodiment 2 of the present invention. 1 is an information carrier, 2 is an optical head, 3 is first phase adjustment means, 4 is second phase adjustment means, 5 is phase adjustment amount setting means, 6 is phase difference detection means, 7 is offset correction learning means, Reference numeral 8 denotes tracking control means, 9 denotes first switching means, 10 denotes a driver, 11 denotes third phase adjusting means, 12 denotes fourth phase adjusting means, and 13 denotes conversion gain setting means. Further, the optical head 2 includes an LD 21, a BS 22, an actuator 23, a lens 24, and a photoelectric conversion unit 25. Further, the phase difference detecting means 6 includes a first adding means 61, a second adding means 62, a first comparator 63, a second comparator 64, a phase comparator 65, a phase difference-voltage converting means 66, a second Of the switch means 67. Furthermore, the offset correction learning means 7 includes a controller 72, an offset measuring means 73, an offset adjusting means 74, and a reproduction level measuring means 75.
[0081]
Next, the operation of the optical information reproducing apparatus according to the second embodiment will be described with reference to FIG. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts. The operation differs from the optical information reproducing apparatus of FIG. 1 in the offset correction learning. Hereinafter, the offset correction learning operation will be described with reference to the offset correction learning algorithm shown in FIG.
[0082]
When the offset correction learning mode is activated (S30), the drive controller that controls the entire device (not shown) sets an initial value parameter in the drive (S31), turns on the LD, and then focuses the light spot on the information carrier. The operation is performed up to the control (S32).
[0083]
Then, the detection gain of the entire tracking error detection system is made substantially constant. Originally, the detection gain of the tracking error detection system fluctuates due to variations in characteristics of the optical head, information carrier, electric circuit, and the like. Therefore, the first offset and the electrical offset also vary depending on the detection gain. In order to suppress this and construct a more reliable tracking error detection system, it is necessary to make the detection gain substantially constant.
[0084]
This sequence is realized by making the amplitude of the tracking error signal output from the phase difference-voltage conversion means 66 substantially constant. The specific operation starts with the reproduction level measuring means 75 measuring the output amplitude from the phase difference / voltage converting means 66 (S33) and determining whether or not the result is within an allowable range (S34).
[0085]
If the determination result does not satisfy the allowable value, the controller 72 changes the conversion gain of the phase difference-voltage conversion unit 66 via the conversion gain setting unit 13 (S35), and again changes the output level of the phase difference-voltage conversion unit 66. The process returns to the detecting step (S33). As described above, the loop of S33 → S34 → S35 → S33 is repeated until the determination result satisfies the allowable value, whereby the amplitude of the tracking error signal output from the phase difference / voltage conversion unit 66 is made substantially constant.
[0086]
Next, an electrical offset generated in a circuit for detecting a tracking error is canceled. This is necessary to more accurately detect the first offset depending on the pit depth and the lens position, which is a problem in obtaining the tracking error signal by the phase difference method.
[0087]
In order to cancel the electric offset, the controller 72 stops the operation of the phase comparison means 65 (S36). In this state, the offset measuring unit 73 measures the output of the offset adjusting unit 74 and obtains an electrical offset (S37). Then, the controller 72 determines whether or not the measurement result is within the allowable range (S38).
[0088]
If the determination result does not satisfy the allowable value, the controller 72 adjusts the output level of the phase difference / voltage conversion means 66 by the offset adjustment means 74 (S39), and returns to the step of measuring the electrical offset again (S37). Thus, the electric offset depending on the detection circuit is canceled by repeating the loop of S37 → S38 → S39 → S37 until the determination result satisfies the allowable value.
[0089]
Next, after canceling the operation stop of the phase comparison means 65 (S40), the controller 72 selects the mode 1 and uses the output of the controller 72 as an input signal to the driver 10 via the first switch means 9. At the same time, the second switch means 67 is controlled to output the output B 'of the second phase adjusting means 4 to the first adding means 67 and the output C' of the third phase adjusting means 5 to the second adding means 68. It is set so that each is input (S41).
[0090]
Thereafter, the lens 24 is driven inward by the control of the controller 72 (S42). In this state, the output level of the phase difference / voltage conversion means 66 is detected by the offset measurement means 73 (S43), and the controller 72 determines whether or not the result satisfies an allowable value (S44).
[0091]
If the determination result does not satisfy the allowable value, the controller 72 individually changes the phase adjustment amount of each phase adjustment unit via the phase adjustment amount setting unit 5 (S45), and again outputs the output level of the phase difference-voltage conversion unit 66. Returns to the step of detecting (S43). In this way, by repeating the loop of S43 → S44 → S45 → S43 until the determination result satisfies the allowable value, the optimum amount of phase adjustment for each phase adjusting means when the lens is displaced toward the inner peripheral side is obtained. Then, the value is stored (S46).
[0092]
Next, the controller 72 drives the lens 24 to the outer peripheral side (S47). In this state, the output level of the phase difference-voltage conversion means 66 is detected by the offset measurement means 73 (S48), and the controller 72 determines whether or not the result satisfies an allowable value (S49).
[0093]
If the determination result does not satisfy the allowable value, the controller 72 individually changes the phase adjustment amount of each phase adjustment unit via the phase adjustment amount setting unit 5 (S50), and again outputs the output level of the phase difference-voltage conversion unit 66. Returns to the step of detecting (S48). In this way, by repeating the loop of S48 → S49 → S50 → S48 until the determination result satisfies the allowable value, the optimum phase adjustment amount for each phase adjusting means when the lens is displaced to the outer peripheral side is obtained. Then, the value is stored (S51).
[0094]
The difference between the inner-side optimum phase adjustment amount and the outer-side optimum phase adjustment amount stored for each phase adjusting means is determined, and it is determined whether or not the difference satisfies an allowable value (S52). If the determination result does not satisfy the allowable value, the controller 72 obtains an average value of the inner peripheral side optimal phase adjustment amount and the outer peripheral side optimal phase adjustment amount stored for each phase adjusting unit, and the like. This value is set to each phase adjusting means via (S53). After the setting, the process returns to S42, and the operations of S42 to S53 are repeated until the difference between the inner peripheral side optimal phase adjustment amount and the outer peripheral side optimal phase adjustment amount satisfies an allowable value.
[0095]
After optimizing the amount of phase adjustment of each phase adjusting means as described above, the operation shifts to an operation of detecting a tracking error signal. The controller 72 selects the mode 2 and controls the second switch means 67 to exchange the input signals to the first addition means 61 and the second addition means 62. The output C ′ of the third phase adjusting means 11 and the output B ′ of the second phase adjusting means 4 are input to one input of the second adding means 62. As a result, the first adding means 61 outputs (A '+ C'). Further, the second adding means 62 outputs (B '+ D').
[0096]
The first comparator 63 binarizes the output (A '+ C') of the first adding means 61, and the second comparator 64 converts the output (B '+ D') of the second adding means 62 to binary. Become The phase comparison means 65 detects a phase difference between the output of the first comparator 63 and the output of the second comparator 64. The output of the phase comparison means 65 is time information, which is converted into an electric signal by the phase difference / voltage conversion means 66 to obtain a tracking error signal by a phase difference method.
[0097]
Finally, fine adjustment is performed so that the amplitude of the tracking error signal output from the phase difference-voltage conversion means 66 becomes a predetermined level. The output level is measured from the phase difference / voltage conversion means 66 by the reproduction level measurement means 75 (S55), and it is determined whether or not the result is within an allowable range (S57). If the determination result does not satisfy the allowable value, the controller 72 changes the conversion gain of the phase difference / voltage conversion unit 66 via the conversion gain setting unit 13 (S57), and again changes the output level of the phase difference / voltage conversion unit 66. The process returns to the detecting step (S55).
[0098]
In this manner, the loop of S55 → S56 → S57 → S55 is repeated until the determination result satisfies the allowable value, thereby making the amplitude of the tracking error signal output from the phase difference / voltage conversion unit 66 constant and satisfying the allowable value. At this point, the offset correction learning mode ends (S58).
[0099]
The tracking error signal after the end of the offset correction learning mode indicates a difference between the target position of the light spot and the current position, that is, an error amount, and the tracking control means 8 controls the light spot position so as to cancel the error amount. I do. The control of the light spot position is realized by the driver 10 driving the actuator 23 based on the output of the tracking control means 8 to control the position of the lens 24 in the radial direction. Therefore, the controller 72 sets the output of the tracking control unit 8 via the first switch unit 9 so as to be input to the driver 10.
[0100]
In FIG. 3, as in the first embodiment, the second switch means 67 is arranged between the second and third phase adjusting means and the first and second adding means. It suffices if the phase difference between (A '+ B') and (C '+ D') or the phase difference between (A '+ C') and (B '+ D') can be detected at 65.
[0101]
Further, the phase difference-voltage conversion means 66 is means for converting time information, which is a phase difference, into an electric signal, and may have any configuration as long as the conversion gain is variable. Generally, this can be realized by using a drive current variable charge pump and an LPF. In this case, there is also an advantage that the drive current can be controlled by a DAC or the like. As another configuration, there is a method in which the LPF is configured by an active filter and the gain is variable.
[0102]
In the optical information reproducing method and apparatus configured as described above, there is no electric offset generated in the detection circuit, and the amplitude of the tracking error signal is corrected by correcting the gain of the entire tracking error detection system to a predetermined value. Can be adjusted to a predetermined level, and the first offset depending on the pit depth and lens position, which has been a problem in obtaining the tracking error signal by the phase difference method, can be directly detected. Since the amount of phase adjustment of each phase comparison means can be optimized by simple repetitive control, it is possible to realize a tracking error signal detection system that is offset-free and has a constant detection gain, thereby stabilizing the tracking control system and improving the reliability of the device. I do.
[0103]
Also, the setting of the optimal phase adjustment amount of each phase adjusting means that changes according to the reproduction speed can be dealt with by the above-described offset correction learning algorithm without changing the hardware, as in the first embodiment.
[0104]
【The invention's effect】
The present invention is configured as described above, and has the following effects.
[0105]
By adding only a few blocks to the conventional optical reproducing apparatus for switching the object to be compared by the phase comparing means, depending on the pit depth and the lens position, which were problems in obtaining the tracking error signal by the phase difference method. The phase difference information between the two signals obtained by dividing the generated far field pattern of the reflected light from the information carrier in the tangential direction of the information track can be directly detected as a voltage value. Since the amount of phase adjustment of the phase comparing means can be optimized, an offset-free tracking error signal detection system can be realized, and the reliability of the device is improved.
[0106]
Further, by switching the object to be compared by the phase comparison means according to the output from the offset correction learning means, it is possible to reliably control the offset correction and the reproduction of the tracking error signal.
[0107]
Further, in the other optical reproducing method and apparatus according to the present invention, this can be canceled by means for correcting an electric offset generated in the tracking error signal detecting circuit, and the gain of the entire tracking error detecting system is corrected. Since the amplitude of the tracking error signal can be made constant by the means, the tracking control system becomes more stable and the reliability of the device is further improved.
[0108]
Also, since the phase difference-voltage conversion means is composed of a charge pump and an LPF, and the conversion gain setting means is configured to change the drive current of the charge pump, the drive current can be controlled by a DAC suitable for LSI. It becomes.
[0109]
Furthermore, the conversion gain setting means is constituted by means for setting the gain of the LPF. If the LPF is an active filter type suitable for LSI, it can be easily controlled by the controller. The use of an LSI reduces variations between elements for setting a gain, improves the accuracy of gain setting, and improves the quality of a tracking error signal. As described above, the gain setting of the conversion gain setting means can be controlled via the controller by adding software that does not affect the development cost, instead of hardware, so that there is also an advantage in terms of device cost.
[0110]
Further, the offset itself can be measured instead of calculating the offset from the waveform symmetry of the tracking error signal as in the related art, so that the detection accuracy is not impaired even if it is not an expensive high-speed ADC.
[0111]
Further, an electrical offset generated in the circuit can be canceled, and a more reliable tracking error detection system can be constructed.
[0112]
Further, the amplitude of the tracking error signal can be finely adjusted by adjusting the phase difference-voltage conversion gain.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical information reproducing apparatus according to a first embodiment.
FIG. 2 shows an offset correction learning algorithm by an offset correction learning unit of the optical information reproducing apparatus according to the first embodiment.
FIG. 3 is a block diagram of an optical information reproducing apparatus according to a second embodiment.
FIG. 4 shows an offset correction learning algorithm by an offset correction learning unit of the optical information reproducing apparatus according to the second embodiment.
FIG. 5 is a diagram illustrating a principle of detecting tracking error information by a phase difference method.
FIG. 6 is a diagram illustrating a principle of occurrence of an offset generated in a tracking error signal depending on a pit depth.
FIG. 7 is a diagram showing a conventional optical information reproducing apparatus.
FIG. 8 shows an offset correction learning algorithm by the offset correction learning means of the conventional optical information reproducing apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Information carrier, 2 optical head, 3 1st phase adjustment means, 4 2nd phase adjustment means, 5 phase adjustment amount setting means, 6 phase difference detection means, 7 offset correction learning means, 8 tracking control means, 9th 1 switch means, 10 driver, 11 third phase adjustment means, 12 fourth phase adjustment means, 13 conversion gain setting means, 21 laser diode, 22 beam splitter, 23 actuator, 24 lens, 25 photoelectric conversion means, 61 First adder, 62 Second adder, 63 First comparator, 64 Second comparator, 65 Phase comparator, 66 Phase difference-voltage converter, 67 Second switch, 71 Waveform symmetry measurement Means, 72 controller, 73 offset measuring means, 74 offset adjusting means, 75 reproduction level measuring means

Claims (4)

An optical information reproducing apparatus in which a light spot traces an information track recorded as an information pit string on an information carrier and reads recorded information,
Dividing a far field pattern of light reflected by the information carrier in a direction perpendicular to a tangential direction of the information track, and disposing a first photodetector and a second photodetector in one of the vertically divided ones; A third photodetector is arranged on the other vertically divided side so as to be diagonal to the first photodetector, and a fourth photodetector is arranged diagonally to the second photodetector. Photoelectric conversion means in which a photodetector is arranged;
First to fourth phase adjusting means for individually adjusting the phase of each of the outputs from the first to fourth photodetectors;
Offset correction learning means for adjusting the first to fourth phase difference adjustment means,
A first sum signal obtained by adding an output from the first phase adjusting unit and an output from the second phase adjusting unit; an output from the third phase adjusting unit and a signal from the fourth phase adjusting unit. Or the third sum signal obtained by adding the output from the first phase adjusting means and the output from the third phase adjusting means to the second sum signal obtained by adding the outputs of the second sum signal and the second sum signal. Phase difference detection means for detecting a phase difference between an output from the phase adjustment means and a fourth sum signal obtained by adding the outputs from the fourth phase adjustment means;
Switching means for switching whether the phase difference detection means detects the phase difference between the first sum signal and the second sum signal or the third sum signal and the fourth sum signal; Prepare,
When adjusting the first to fourth phase difference adjusting means, the switching means selects the first sum signal and the second sum signal as targets for detecting the phase difference by the phase difference detecting means. Then, the first to fourth phase difference adjusting means are adjusted by the offset correction learning means so as to cancel the phase difference output from the phase difference detecting means,
When obtaining the tracking error information, the switching means selects the third sum signal and the fourth sum signal as targets for detecting the phase difference by the phase difference detection means ,
The offset correction learning means,
Offset adjustment means for adjusting the electrical offset superimposed on the output from the phase difference detection means,
Offset measuring means for measuring an output from the offset adjusting means and obtaining an electrical offset,
Reproduction level measuring means for measuring the output amplitude from the offset adjusting means,
A control unit for controlling the phase difference detecting unit, the offset adjusting unit, and the phase adjusting unit based on an output from the offset measuring unit and an output from the reproduction level measuring unit. Optical information reproducing device. The phase difference detecting means detects the phase difference between the signals by the phase comparing means, converts the phase difference into a voltage by a low-pass filter (hereinafter referred to as “LPF”), and varies the gain of the LPF by changing the gain. 2. The optical information reproducing apparatus according to claim 1, further comprising a configuration for changing a conversion gain of converting the phase difference into a voltage. The phase difference detection means detects the phase difference between the two signals by the phase comparison means, converts the phase difference into a voltage by the charge pump and the LPF, and varies the drive current of the charge pump or the gain of the LPF by changing the voltage. 2. The optical information reproducing apparatus according to claim 1, further comprising a configuration for changing a conversion gain of converting the phase difference into a voltage. In an optical information reproducing method in which a light spot traces an information track recorded as an information pit row on an information carrier and reads recorded information,
Initializing when the offset correction learning mode is activated;
Dividing a far field pattern of light reflected by the information carrier in a direction perpendicular to a tangential direction of the information track, and disposing a first photodetector and a second photodetector in one of the vertically divided ones; A third photodetector is arranged on the other vertically divided side so as to be diagonal to the first photodetector, and a fourth photodetector is arranged diagonally to the second photodetector. A first to fourth phase adjustment output, in which a photodetector is arranged, and the phases of the respective outputs from the first to fourth photodetectors are individually adjusted, the first phase adjustment output and the first A first phase comparison mode for detecting a phase difference between a first sum signal obtained by adding the two phase adjustment outputs and a second sum signal obtained by adding the third and fourth phase adjustment outputs. Selecting
Driving the lens in one direction of the inner and outer peripheries of the information carrier;
Detecting a phase difference in the first phase comparison mode;
The phase of the output from the first to fourth photodetectors so that the output from the step of detecting the phase difference in the first phase comparison mode cancels the phase difference detected in the first phase comparison mode. A one-way adjustment step of adjusting
Driving the lens in the other direction on the inner and outer circumferences of the information carrier;
Driving in the other direction to cancel the phase difference detected in the first phase comparison mode by the output from the step of detecting the phase difference in the first phase comparison mode. A different direction adjustment step for adjusting the phase of each output from the photodetector,
Adjusting the adjustment amount in the one direction adjustment step and the other direction adjustment step,
further,
After the step of adjusting the adjustment amount in the one-direction adjustment step and the other-direction adjustment step,
Phase difference between a third sum signal obtained by adding the first phase adjustment output and the third phase adjustment output, and a fourth sum signal obtained by adding the second phase adjustment output and the fourth phase adjustment output Selecting a second phase comparison mode for detecting
Adjusting the amplitude of the tracking error signal ,
The step of performing the initial setting,
Detecting a phase difference between a third sum signal obtained by adding the first phase adjustment output and the third phase adjustment output, and a fourth sum signal obtained by adding the second phase adjustment output and the fourth phase adjustment output; Selecting a second phase comparison mode to perform;
Adjusting the reproduction level of the phase difference output detected in the second phase comparison mode to be within an allowable value;
Adjusting an electrical offset superimposed on the phase difference output so as to be within an allowable value .

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